全文获取类型
收费全文 | 43472篇 |
免费 | 8955篇 |
国内免费 | 12088篇 |
专业分类
测绘学 | 4513篇 |
大气科学 | 8504篇 |
地球物理 | 10002篇 |
地质学 | 23037篇 |
海洋学 | 6652篇 |
天文学 | 1425篇 |
综合类 | 4616篇 |
自然地理 | 5766篇 |
出版年
2024年 | 180篇 |
2023年 | 702篇 |
2022年 | 2128篇 |
2021年 | 2466篇 |
2020年 | 2054篇 |
2019年 | 2319篇 |
2018年 | 2586篇 |
2017年 | 2331篇 |
2016年 | 2620篇 |
2015年 | 2533篇 |
2014年 | 2816篇 |
2013年 | 2967篇 |
2012年 | 3031篇 |
2011年 | 3069篇 |
2010年 | 3149篇 |
2009年 | 2945篇 |
2008年 | 2820篇 |
2007年 | 2675篇 |
2006年 | 2189篇 |
2005年 | 1954篇 |
2004年 | 1486篇 |
2003年 | 1252篇 |
2002年 | 1245篇 |
2001年 | 1284篇 |
2000年 | 1380篇 |
1999年 | 1625篇 |
1998年 | 1230篇 |
1997年 | 1151篇 |
1996年 | 1062篇 |
1995年 | 928篇 |
1994年 | 792篇 |
1993年 | 715篇 |
1992年 | 573篇 |
1991年 | 456篇 |
1990年 | 336篇 |
1989年 | 308篇 |
1988年 | 274篇 |
1987年 | 160篇 |
1986年 | 147篇 |
1985年 | 93篇 |
1984年 | 99篇 |
1983年 | 77篇 |
1982年 | 66篇 |
1981年 | 57篇 |
1980年 | 33篇 |
1979年 | 37篇 |
1978年 | 11篇 |
1977年 | 11篇 |
1958年 | 30篇 |
1954年 | 11篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
Yo-ichiro Otofuji Takaaki Matsuda Ryo Enami Koji Uno Katsuhiko Nishihama Li Su Ruslan G. Kulinich Petr S. Zimin Anatoly P. Matunin Vladimir G. Sakhno 《Tectonophysics》2002,350(3)
We present paleomagnetic results of Paleocene welded tuffs of the 53–50 Ma Bogopol Group from the northern region (46°N, 137°E) of the Sikhote Alin volcanic belt. Characteristic paleomagnetic directions with high unblocking temperature components above 560 °C were isolated from all the sites. A tilt-corrected mean paleomagnetic direction from the northern region is D=345.8°, I=49.9°, α95=14.6° (N=9). The reliability of the magnetization is ascertained through the presence of normal and reversed polarities. The mean paleomagnetic direction from the northern region of the Sikhote Alin volcanic belt reflects a counterclockwise rotation of 29° from the Paleocene mean paleomagnetic direction expected from its southern region. The counterclockwise rotation of 25° is suggested from the paleomagnetic data of the Kisin Group that underlies the Bogopol Group. These results establish that internal tectonic deformation occurred within the Sikhote Alin volcanic belt over the past 50 Ma. The northern region from 44.6° to 46.0°N in the Sikhote Alin volcanic belt was subjected to counterclockwise rotational motion through 29±17° with respect to the southern region. The tectonic rotation of the northern region is ascribable to relative motion between the Zhuravlevka terrane and the Olginsk–Taukhinsk terranes that compose the basements of the Sikhote Alin volcanic belt. 相似文献
992.
993.
Shijie Qu Shuhua Hao Guangping Chen Baohui Li Guangzeng Bian 《Fragblast: International Journal for Blasting and Fragmentation》2002,6(1):85-103
Blast design is a critical factor dominating fragmentation and cost of actual bench blasts. However, due to the varying nature of rock properties and geology as well as free surface conditions, reliable theoretic formulae are still unavailable at present and in most cases blast design is carried out by personal experience. As an effort to find a more scientific and reliable tool for blast design, a computer-aided bench blast design and simulation system, the BLAST-CODE model, is developed for Shuichang surface mine, Mining Industry Company of the Capital Iron and Steel Corporation Beijing. The BLAST-CODE model consists of a database representing geological and topographical conditions of the mine and the modules Frag + and Disp + for blast design and prediction of resultant fragmentation and displacement of rock mass. The two modules are established in accordance with cratering theory qualitatively and modified quantitatively by regression of the data collected from 85 bench blasting practices conducted in 3 mines of the Shuichang surface mine. Blasting parameters are selected based upon quantitative and comprehensive evaluation on the effect of the factors such as rock properties, geology, free surface conditions and detonation characteristics of the explosive products in use. In order to ensure practicality and reliability of the system, the BLAST-CODE model allows automatic adjustment to the selected parameters such as burden B and spacing S as well as explosive charge amount Q of any blasthole under irregular topographic and/or varying blastability conditions of the rock mass to be blasted. Simulation of the BLAST-CODE model includes prediction of fragmentation and displacement that are demonstrated in terms of swell factor, characteristic rock size x c and size distribution coefficient n by Rossin-Ramler's equation, and 3-dimentional muck pile profile. The BLAST-CODE model also permits interactive parameter selection based on comparison of the predicted fragmentation and displacement as well as the cost for drilling, explosives, and accessories until the most effective option can be selected. 相似文献
994.
995.
The Hongzuisi Section in Lanzhou area is used to infer the paleoclimate since the late glacial epoch. Through combined analysis of organic carbon isotope and CaCO3 content, paleoenvironment evolution of Hongzuisi Section since the late glacial epoch is discussed. There were changes in both drymoist and warm-cold. Especially the climate changes can be compared with synchronous sections of other areas, which provides useful information for our future forecast. 相似文献
996.
997.
998.
999.
1000.